Pectic materials and method of preparing same



Mme 2Q, 1948.

0.5 N ALKALI (MILLILITERS) N U! 1/r mnvurss') H. s. @WENS ETAL.

PEGTIC MATERIALS AND METHOD OF PREPARING SAME Filed manual, 1944 ljigiEffect of Temperu-i-ure on Rore of Demtho lotion Orange Pe eL. 125 grams40 50 MINUTES Effect of pH. on reciprocal of Hulf-Reocfion Time HC.OWEN$ W;D. MACLAY Patented June 29, 1948 I UNITED STATES PATENT OFFICE?ECTIC MATERIALS AND METHOD OF PREPARING SAME Harry S. Owens and WilliamDayton Maclay, Berkeley, Calif.. asslgnors to the United States ofAmericans represented by the Secretary of Agriculture Application March31, 1944, Serial No. 529,016

4 Claims. (01. 195-30) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) for preparing a series ofpartially demethoxylated pectins (pectinic acids) of high molecularweight.

We have found that a series of pectic materials of varying methoxylcontent and of high molecular weight can be prepared from citrus peel orapple pomace (e. g., citrus peel or apple pomace which has not beensubjected to treatment such as to inactivate the enzyme content), orfrom mixtures of citrus peel or apple pomace withother pectin-containingmaterials or with pectin, by adjusting the pH of the reaction mixture soas to 011- tain active enzymic action of the pectin-esterase present inthe citrus peel or apple pomace, and then extracting the resultingpectic materials at an acidic pH in the presence of a calciumcomplex-forming agent according to the process described by Maclay andNlelsenin their application for patent Serial No. 529,015, filed March31, 194 now Patent 2,375,376.

Our process comprises forming an aqueous slurry of: (1) dispersed citruspeel or apple pomace 30 or a newly-made aqueous extract of disintegratedcitrus peel; (2) a mixture of a pectin-containing material and dispersedcitrus peel or apple pomace; (3) a mixture of pectin and dispersedcitrus peel or apple pomace; or (4) a mix- 35 ture of a newly-madeaqueous extract of disintegrated citrus peel and pectin or apectincontaining material. This aqueous slurry is then adjusted to atemperature within the range 0 to 60 C., preferably below 45 C., and 40suificient sodium hydroxide solution is added to bring the reactionmixture to a pH of 6 to 10, preferably 8 to 10. Under these conditions,the peetin-esterase present in the citrus peel or apple pomacedemethoxylates the pectin present, either 2 in situ or as free pectin,in the reaction mixture. The addition of alkali is continued at a ratewhich will maintain the proper pH until the amount of alkali necessaryto yield a pectinic acidofthe desired methoxyl content has been added.The dispersion is then rapidly acidified to a pH of about 3 with astrong acid, and may be heated to boiling to destroy the catalystspresent. The pulp which is obtained at this point in the process may bepressed or filtered and dried for storing, if

desired.

The extraction is accomplished by adding about 0.5 percent of sodiumhexametaphosphate to the blanched dispersion and heating at boilingtemperature for about 10 tominutes. Recovery is efl'ected by filteringthe extraction mixture, and isolating the pectinic acid in the usualmanner. The resulting products are very fibrous in nature and theirsolutions exhibit very high viscosities.

Our invention is illustrated by the following examples:

Exmrs I that value for 4.8 minutes by gradual addition of 40 ml, of0.5N-sodium hydroxide. The dispersion was then rapidly acidified to a pHof 3 by addition of 18N-sulfuric acid, and quickly heated to boiling todestroy the catalysts present. At this stage the pulp may be filtered,dried and stored, if desired. The extraction was accomplished by adding6 g. of sodium hexametaphosphate to the blanched dispersion (theaddition would be made to redispersecl pulp if it had been stored afterthe processing above), and heating to boiling for 15 minutes. Thedispersion was then filtered and the liquor was poured into 1 volume of95 percent ethanol. The pectinic acid was filtered, hardened in alcohol,dried and ground. Yield: 9.5 g. or 10.5 percent on basis of dried weightof peel.

Methoxyl content: 3.1 percent.

Examru II 1 kilogram of fresh lemon peel was ground and dispersed in3500 ml. of water at 25 C. 60 ml. of 2N-alkali was added to adjust thepH to 8, 01-

" lowed by the continuous addition of 90 ml. of

0.5N-alkali during 6.5 minutes. The demethoxylation reaction was stoppedby addition or 18N-sulfuric acid to lower the pH of the reaction mixtureto 3. The dispersion was then heated to boiling, 6 g. of sodiumhexametaphosphate was added and the mixture was boiled for minutes. Thepulp Exam III 1 kilogram of fresh grapefruit peel was disintegrated in 5liters of water at 24.5" C. 24 ml. of 2N-alkali was added to adjust thepH to 8. An additional 16 ml. of 2N-alkali was added during a period of2.6 minutes to neutralize the acidic groups formed by virtue of partialdemethoxylation of the pectic material. The dispersion was acidifiedwith 1:1 sulfuric acid to a pH of 3 and heated to boiling. 15 g. ofsodium hexametaphosphate was added and the extraction was continued for15 minutes at boiling temperature. Yield: 16 g. or 9 percent on thebasis of dried weight of peel. Methoxyl content: 5.5 percent.

Exammn IV 500 g. of apple pomace was disintegrated in 2 liters of waterat 25 C. The pH was adjusted to 8 with 2N-alkali. An additional 28 ml.of 0.5N- alkali was added in 21.7 minutes to neutralize the deesterifiedacid groups. The slurry was then acidified to pH 3 by the addition of1:1 sulfuric acid and heated to boiling, and 6 g. of Calgon was added.The extraction was continued for 15 minutes. Yield: 5 g. or 4 percent Onthe basis of total solids. Methoxyl content: 3.2 percent.

EXAMPLE V A mixture of 100 g. of dried apple pomace and 100 g. of freshorange peel was ground in 2500 m1. of water at 25 C., and the pH wasadjusted I to 9 by rapid addition of 2N-alkali, and the dispersion wasmaintained at that pH by the addition of 30 ml. of 0.5N-alkali during aperiod of 13.5 minutes. The reaction mixture was then acidified to a pHof 3 and heated to boiling. 6 g. of sodium hexametaphosphate was addedand the mixture was boiled for 15 minutes. The pulp was then filteredoff and the liquor was precipitated in two volumes of alcohol. Theprecipitate was hardened in alcohol, and then dried and ground.- Yield:10.5 g. or 9.4 percent on basis of dried weight of pomace and peel.Methoxyl content: 3.0percent.

' EXAMPLE VI 6 g. of apple pectin having a methox-yl content of 6percent and 250 g. of ground fresh orange peel were mixed in 1500 ml. ofwater at 25 C.

The mixture was adjusted to a pH of 8 by the addition of 22 ml. of0.5N-sodium hydroxide. Sufficient additional alkali was added todeesterify one-half of the calculated quantity of methoxyl groupspresent. The dispersion was then acidified to a pH of 3, 3 g. of sodiumhexametaphos. phate was added, and extraction was carried out at boilingtemperature for 15 minutes. The pulp obtained was filtered and theresulting liquor was precipitated with alcohol. The pectinic acidrecovered was hardened in alcohol, and then dried and ground. Themethoxyl content was 3.9 percent as compared to a calculated value of3.7 percent.

EXAMPLE VII To 100 g. of thinly sliced lemon peel suspended in 600 ml.of water was added 50 ml. of 0.5N ammonium hydroxide -to adjust the pHto 8.4. An additional 100 ml. of 0.5N ammonium hydroxide was addedduring a period of 20 minutes. The pulp was then pressed and dried.Nitrogen content of product was 2.2 percent.

The proper reaction conditions for carrying out our process areindicated by the following data:

TABLE I Rate of consumption of alkali in minutes at Ml. of 0.5 N-Alkali0 C. 17 C. 25 C. 35 C. 45 C.

1 As measured by the rate of consumption oi alkali by 125 g. ofdisintegrated orange peel in 1500 ml. of water at a pH of 7.

The information shown in Table I is plotted in Figure 1 to illustratethe. rapidity of the reaction. Half-reaction time, calculated on thebasis of average yields and average methoxyl content of pectin isolatedfrom orange peel, is obtained when 8.8 ml. of 0.5N-alkali is added. Anadditional curve for a reaction temperature of C. is plotted in Figure 1to show that the reaction apparently stops at this temperature becauseof denaturation of the enzyme. As indicated by Table I, however, thereaction can be carried out at any temperature from 0 to 45 C. withoutdifficulty. The upper practical limit has been found to be about 60 C.

Rate of consumption of alkali in minutes at-- N-alkali v pH 6.0 pH 6.5pH 7.0 pH 8.0 pH 9.0 pH 10.0 1

1 As measured by the rate of consumption of alkali by 500 g. of orangepeel in 1500 ml. of water at 25 C.

9 35 ml. alkali is approximately equivalent to 50 percentdemethoxylaticn.

Table II, together with Figure 2 which shows the effect of pH onhalf-reaction time, emphacontaining material in the aqueous slurryincreases. It has also been found'that citrus peel disintegrated to afine dispersion in a Waring blender reacts at a rate appreciably greaterthan like peel ground in a meat grinder.

The rate of demethoxylation is also increased by the addition of sodiumhexametaphosphate to the reaction mixture. Thus, a mixture of 400 a. orblanched orange peel, 100 g. of fresh orange peel, and 2000 ml. of wateradjusted to a pH of 8 required 18 minutes for the addition of 40 ml. of0.5N-alkali. When 3 g.

of sodium hexametaphosphate was added, however, only 12 minutes wasrequired, and when 6 g. or the salt was added the reaction time wasreduced to 8 minutes.

I As measured by the rate of consumption of alkali by 126 g. peel orpomaoe in 1500 ml. of water at 25 C. and at pH 7.

Table III indicates that oranges, grapefruit and lemons contain aboutthe same ratio of enzyme to pectin, since the rate of reaction is nearlythe same for each fruit'in the early stages of the reaction. Thegrapefruit and lemon peel used in the experiments from which the data inTable III were obtained contained more pectin than the orange peel used,which accounts for the fact that in the case of the orange peel the highrate of reaction did not continue for as long a period of time.

It appears from the results obtained with apple pomace that appleseither contain a smaller quantity of enzyme or that the enzyme ispartially removed from the field of action by the presence of othersubstances, such as tannins.

The efiect of heat on the stability of the enzyme is shown in Table IV.The comparison is between unheated orange peel and orange peelsteam-blanched for 5 minutes. In each case the tests were conducted with500 g. of orange peelblanched or unblanched in 1500 ml. of water at 25C. and a pH of 9.

TABLE IV Effect of blanching on rate of demethozrylatio'n alkali inminutes Ml. oi 0.5 N-Alkali Unblanched Blanched Rate of consumption of lme astases? senseless PH 5 The nature of the product obtained can becontrolled to some extent by the procedure used during demethoxylationand extraction. This is illustrated by Tables VI and VII below, whichshow the efiect of the pH maintained during demethoxylation and ofvarying extraction pro cedure on the viscosity of the product obtained.The viscosity measurements were made with onepercent solutions of theproducts at 25 C. and pH 7 in a Stormer viscosimeter.

TABLE VI Efiect of pH maintained during demethozylation on viscosity ofproduct d Conttzitioziz of eme oxy t on Product from MeO, 'n cent-i peelof- Per Cent poises pH at? Orange. 6 101 25 s 2. e 23 8 4. 8 25 10 3. 131 9 4. 2 25 2. 7 33 Team VII Effect of extraction procedure onviscosity of product 1 Sodium PH Temp., Time, hexametan centi- 0. min.phosphate poises g./500 g. peel -98 15 15 11 95-98 60 l5 13 95-98 30 l516 95-98 15 15 13 95-98 15 G 28 95-98 30 6 23 95-98 60 6 16 25 60 6 2195-98 15 6 7 70 20 6 18 25 60 6 36 1 In each case the demethoxylationwas performed on orange peel at a pH of 8.

Our invention is not limited to the pectin source materials used asillustrations in the examples and tabulated data set forth above, but isapplicable generally to pectin-containing materials, such as carrots,pea. hulls, sugar beets, quinces, grapes, and so forth. Nor is ourinvention limited to products of a specified methoxyl content. Pectinicacids may be prepared by the methods disclosed herein ranglng'in mthoxylcontent from that of pectic acid (provided an alkaline extraction mediumis used) to the methoxyl content of the pectin in the pectin-containingsource material.

Having thus described our invention, we claim:

1. The process of preparing pectinic acids of low methoxyl content whichcomprises subjecting an aqueous dispersion of citrus peel to partialde-methoxylation by enzyniic hydrolysis, said hydrolysis being attainedby adding an alkali to the dispersion and maintaining the dispersion ata pH of 6 to 10 and a temperature of C. to 60 C. until the low-methoxylpectinic acids are formed the enzymic demethoxylation being in thepresence of a small amount of sodium hexametaphosphate.

2. The process according to claim 1 wherein the pH is maintained at 8 to10 and the temperature from C. to C.

3. The process of partially demethoxylating pectin which comprisesforming an aqueous dispersion at a. temperature of about 0 to C. ofcitrus peel, adjusting the dispersion to a pH of 6 to 10 with alkalisolution, adding additional alkali solution at a rate which willmaintain the pH within the range from 6 to 10 until the amount of alkalinecessary to obtain the desired degree of demethoxylation has beenadded, the demethoxylation being in the presence of a small amount oisodium hexametaphosphate. then rapidly acidifying the dispersion with astrong acid and quickly heating to boiling to destroy the catalystspresent." a

4. The process described in claim 3 in which the pectinic acid formed isextracted from the acidic dispersion containing sodiumhexametaphosphate. v

HARRY s. OWENS. WILLIAM DAYTON MACLAY.

- REFERENCES crrnn The following references are of record in the tile 0!this patent:

UNITED STATES PATENT Number Name Date Re. 21,077 Wilson May 9, 19391,513,615 Leo Oct. 28, 1924 2,132,065 Wilson Oct. 4, 1938 2,133,273 CoxOct. 18, 1938 2,349,138 Bryant May 16, 1944 2,358,430 Willaman Sept. 19,1944 FOREIGN PATENTS Number Country Date 541,528 Great Britain Dec. 1,1941

